The invention generally relates to the synthesis of naphthalenic compounds, and more particularly relates to the synthesis of 1,5 dimethylnaphthalenes and the use of these compounds and their synthesis intermediates.
Polymers based on dimethyl-2,6-naphthalenedicarboxylate (2,6-NDC) are known to be useful in a wide variety of commercial applications.
Films made from 2,6-NDC-based polymers exhibit strength and thermal properties which are superior to films and fibers made from other polymers such as polyethyleneterephthalate (PET). These enhanced properties have led to the use of 2,6-NDC-based polymers in camera films and magnetic recording tapes as well as electrical and electronic components.
2,6-NDC-based polymers also exhibit high resistance to the diffusion of gases such as carbon dioxide, water vapor and oxygen. This resistance to gas diffusion makes these polymers useful in films and containers for a wide variety of food and beverage packaging applications.
The superior physical strength of 2,6-NDC-based polymers also renders these polymers useful in physically demanding applications such as cords for automobile and motorcycle tires.
Unfortunately, the commercial scale synthesis of 2,6-NDC is a complex, multi-step process, which can result in a relatively high price per pound for 2,6-NDC when compared to other polymers.
The synthesis of 2,6-NDC typically includes several steps. In a typical synthesis, orthoxylene and butadiene are reacted over an alkali metal or other catalyst to yield a 5-orthotolylpentene (5-OTP) alkenylation product. The 5-OTP is then cyclized over an acid catalyst to yield 1,5 dimethyltetralin (1,5-DMT). The 1,5 DMT is dehydrogenated over a noble metal or some other dehydrogenation catalyst to yield 1,5-dimethylnaphthalene(1,5-DMN), which is subsequently isomerized to produce 2,6-dimethylnaphthalene (2,6-DMN).
Once 2,6-DMN has been produced, it is oxidized to produce 2,6-naphthalene dicarboxylic acid (2,6-NDA), which is subsequently esterified to produce 2,6-NDC. This 2,6-NDC can then be polymerized in the presence of, for example, ethylene glycol, to produce polyethylenenaphthate (PEN) useful as a monomer or comonomer in applications such as those discussed above.
The foregoing seven step process to produce PEN demands that every synthesis step be selective and produce high yields of the desired end product if NDC is to be manufactured in a commercially economically successful manner.
What is needed is a naphthalenic monomer that can be produced more efficiently and at low cost.
We find that the economic viability of naphthalenic monomers can be increased in many applications by producing a 1,5-NDC-based material rather than a 2,6-NDC-based material. Elimination of the isomerization reaction and 2,6-DMN purification required to convert 1,5-DMN to 2,6-DMN reduces process cost, increases yield and can increase plant capacity where the isomerization reaction or purification of the isomerized product is a production limiting step. By identifying uses for several intermediates in the 1,5-NDC synthesis reaction, we find that the production of these intermediates need not be carried out in the specific proportion required to manufacture the 1,5-NDC end product material, thereby making the sizing of equipment less critical, and increasing the economic viability of an NDC polymer plant as overproduction of intermediates can be accommodated by diverting excess material to other end uses.
Additionally, we believe that the unique physical and chemical properties of 1,5-NDC make 1,5-NDC a preferred material over other monomers such as isophthalic acid in many applications, thereby increasing demand for NDC materials generally.